Spring balanced adjustable blackboard



Aug. 30, 1966 F. BONG 3,269,035

SPRING BALANCED ADJUSTABLE BLACKBOARD Filed NOV. 26, 1963 2 Sheets-Sheet l I V ENTOR Aug. 30, 1966 F. BONG SPRING BALANCED ADJUSTABLE BLACKBOARD 2 Sheets-Sheet 2 Filed Nov. 26, 1963 Fig. 5

INVENTOR.

United States Patent nice 3,2d9fi35 Patented August 3ft, lihfifi 3 269 0335 SPRING BALANCED ADJlJSTABLE BLACKEQARD Friedrich Bong, Din-lug A. Warren, 3d Kettwiger Strasse, Essen, Germany FiledNov. 26, 1963, Ser. No. 32643 1 Claim. (Cl. 35--63) The invention refers to a spring-actuated counterpoise for a board adjustable perpendicularly on a wall, e.g. a school blackboard, with cam mechanism between sprlng and board' Whereas by the use of counterpoise weights which set on the board by means of tie members and guide rollers, it can be attained, by means of the appropriate calculation of the counterpoise weight, without anything else, that the board automatically remains stationary at each position of adjustment, this effect is not produced without anything else on replacing the counterpoise weight by springs.

The tension of a spring increases with its length of stretch, so that a blackboard actuated by spring always comes to rest automatically at a predetermined height at which the tension of the spring is exactly equal to the weight of the board.

In order to bring the board to a higher position, an additional force must be applied to the board, and in order to hold it at the new position, special means of holding must be employed, as otherwise the board automatically returns to the afore-mentioned equilibrium position.

These requirements heretofore have made the use of blackboards compensated by means of springs awkard, apart from the fact, that with an unintentional releasing of the means of holding or clamping, the board can undergo undesirable movements.

To bring about a full counter-balance at all heights of the blackboard there is used a cam mechanism known, for example, in drawing desks, in which the rollers carrying the bearing cords are connected to revolving cam bodies, on the perimeter surfaces of which springloaded cords run. The cams are so formed that the cords, with progressive tensioning of the spring, act on the cam elements with a lever arm which becomes smaller, so that the momentum acting on the revolving cam bodies, and along with it, the portion of the spring resistance acting on the board, is always equal to the weight of the board.

There heretofore proposed forms of construction of this spring tension compensation with revolving cam bodies do not, however, allow of their use for adjustable wall blackboards, as these must exhibit a minimum possible distance from the wall and must exhibit no projecting parts, especially at the bottom, which hinder the activities of the teacher or the pupils in front of the board, nor, in the vertical movement of the board, a-ny mechanism, such as movable levers, springs, or the like, which distract the attention of the pupil during instruction. These conditions are fulfilled by the adjustable wall blackboard in accordance with the invention in that, at least one of the two bearing cords acting on the ends of the boards leads to a flat pulley, which is firmly attached to an equally. flat cam disc, on the circumference of which there runs a cord which acts on a coil spring, arranged parallel to the plane of the board, and secured to a fixed point.

A simple construction form of this lay-out consists in that one bearing cord is fastened with its free end at a point in one groove of the double-grooved pulley, while perpendicular to the plane of the board, fastened to the framework.

A variation of the aforementioned example of construction with a pulley together with a cam disc attached thereto, consists in that, the bearing cords: are fastened with their ends to the mounting of the board and run on the return pulleys carried on the wall blackboard to a flat, doubleagroov-ed pulley carried on the back on the board, which is firmly attached to a flat cam disc, on the circumference of which runs a cord, which is fastened to a spring, which attached by its other end to the back of the board.

In order, in spite of the higher pull of the spring used, to be able to obtain a minimum distance from the wall, the spring consists of two coil springs arranged alongside each other parallel to the plane of the board.

With heavier weights of board and greater lengths of board, it is recommended that two pulleys with cam discs attached thereto be provided, while the bearing cords acting on the ends of the ends of the board lead to, in each case, a flat pulley, carried on the framework, with firmly attached cam discs, and are so secured to this by their other ends, that, with vertical movement of the board, the pulleys rotate in opposite directions and that on the cam discs of each there runs a cord, the ends of which act on coil springs, which are arranged in a plane parallel to the board and the other ends of each of which are secured to a fixed point in the framework, and the two pulleys are connected to each other by means of a synchronizing cord.

The points of application of the two bearing cords to the wall blackboard are so arranged that the pulleys together with springs, during the up and down movement of the board, remain covered by this. In the form of construction, in which the mechanism is carried on the b ack of the board, this result follows of its own. accord, and independently of the extent of vertical movement of the board.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which is:

FIG. 1 a partly broken-away front view of the board with a cam disc and an ordinary pulley,

FIG. 2 a top view relative thereto,

FIG. 3 a back view of an example of construction, in which the mechanism is carried on the back of the board itself,

FIG. 4 an example of construction with two pulleys with cam discs attached thereto, and

FIG. 5 a top view relative thereto.

in the embodiment shown in FIGS. 1 and. 2 the board 1 moves in vertical guides 2 of a framework 3 fastened to the Wall or on supports. To this framework are fixed two axles 4-, 5 vertical to the plane of the board. On the axle 4 is carried a double-grooved cord pulley 6, which is rigidly attached to a co-axial cam disc 7. To the ends of the board 1 are applied bearing cords 8 9 by fastening screws 11, 12.

The bearing cord 8 runs over one (13) of the two grooves of the pulley 6 and is fastened to this at the point 1-4. The other bearing cord 9 runs in a clockwise direction over an ordinary pulley 10, carried on the axle 5.

The bearing cord 9 runs in an anti-clockwise direction in the second groove 16 of the pulley 6 and is fastened to this at the point 17, so, that, on vertical movement of the board, the two pulleys 6 and ltl rotate in opposite directions.

To the cam disc 7, in the neighbourhood of its greatest radius, is fastened a tensioning cord 18, at the point 19, which acts on the mid-point 21 of a compensating lever 22, to the ends of which are secured corresponding coil springs 26.

At their other ends the springs are attached to a similar compensating lever 24, of which the mid-point 25 is secured, by means of a length of cord 26 to a fixed point 27 of the framework 3.

In the drawing the board is shown at its highest adjustment position. If it is pulled down, then the two bearing cords 8 and 9 run out from their pulleys in opposite directions. Thereby a pull is given to the tensioning cord 18, which leads to an increased tensioning of the spring 23. The cam disc 7 is now so formed that the radius at any time of the running-off point of the cord from the cam disc diminishes in inverse ratio to the tension of the spring 23, so that the torque exerted by the springs on the pulley 6 remains the same. It is so proportioned that it corresponds to the product of the constant weight of the board and the groove-radius of the pulley 6. From this it follows that the board )1, in any vertical position to which it is moved by hand upwards or downwards, is in equilibrium and remains stationary in that position.

By means of the opposed running on the bearing cord 9 over the two pulleys 6 and 15 a parallel movement of the board is also attained. The points of attachment It, 12 of the bearing cords to the board 1, the extent of the up and down movement of the board and the arrangement of the mechanism on the framework are so selected that, on vertical movement of the wall blackboard no mechanism appears in sight.

In the embodiment shown in FIG. 3 the compensating mechanism is carried on the back of the board 1. On an axle 4 set up on the back of the board a double-grooved circular pulley 6 is carried. The two bearing cords 8 and 9 for the board are secured at their upper end each to a bolt 28 of the stationary carrying and guiding frame 29. They run over reversing pulleys 32 carried on pins 31 at the back of the board and engage in the two grooves 13 and 16 (FIG. 2) of the pulley 6, in which grooves they are fixed at the points 14 and 17. A tensioning cord 18 acts, at the point 19, on the cam disc 7 rigidly fixed to the pulley 6, which is attached to a spring 23, which is secured to the back of the board it by means of an adjusting bolt 33 and a holder 34.

In FIG. 3 the board ll of this construction is shown at its highest position. then the two bearing cords 8, 9, run off, at equal speed, from the cord pulley 6, whereby the cord pulley 6 revolves in a clockwise direction and the spring 23 is stretched through the tensioning cord 18 by means of the cam disc 7.

Here also the cam disc is so formed that the increasing tension of the spring 23 is equalised by the correspondingly diminishing running-off radius of the cam disc 7 and the board remains stationary in any position of vertical movement.

Here special precautions do not have to be taken to prevent the coming into view of moving mechanism, because the mechanism, carried on the back of the board, is continually covered up, and this without taking into account the extent of the vertical movement.

In the embodiment shown in FIGS. 4 and 5, which is especially appropriate to long, heavy movable boards, two double-grooved pulleys 6, 6 are employed, each which is rigidly attached to a cam disc 7, 7 and runs freely on axles 4, 4, arranged vertically to the plane of the board, and fastened to the stationary framework 3.

In one groove of each pulley runs one of the hearing If the board is moved downwards,-

cords 8, 8'. These are fastened at the points 14, 14' of the grooves and are attached by the other ends 11 and 12 respectively to the board I. In the neighbourhood of the point on the circumference with the greatest radius of the cam discs 7, 7 a tensioning cord 18 is attached to each respectively at the points 19 and 19, which is connected to a spring 23, which is attached by means of a length of cord 26, 26' to a fixed point 27, 27' of the framework In FIG. 4 the board is shown at its highest vertical position. If the board is lowered by hand, then the two pulleys 6, 6' revolve in opposite directions in such a way that the tensioning cords 18, 18' are wound up on the cam discs '7, 7 and the increasing tension of the spring 23 is equalled by the correspondingly decreasing radius of the cam discs, so that here too, the adjustable wall blackboard remains stationary in each adjustment position attained.

Round the two pulleys 6, and 6 a synchronous cord 35 can be led in the opposite direction by means of a third groove, by means of which the horizontal positioning of the board can additionally be ensured at each adjustment setting.

As can be seen, in the embodiments of FIGS. 1 and 4, two long coil springs are used in each case. The same thing can also be done in the form of construction in FIG. 3. The two springs 23 are in this manner arranged in a plane parallel to the plane of the board, so that the distance of the board from the wall can be kept smaller than if a single coil spring of equal tension is involved.

What I claim is:

In a school blackboard perpendicularly adjustable in a stationary framework, a circular double grooved pulley, a grooved cam disc securely fastened thereto, both being rotatably mounted on a pin fixed at the back of said blackboard, two reversing pulleys, each rotatably mounted on an end of the blackboard at the back thereof, two bearing ropes each attached with its one end to one side of said stationary framework near the upper end thereof and running downwards and over one of said reversing pulleys into one of the grooves of said double grooved pulley, and means for fastening the other end of said bearing ropes in the related grooves,

a tension spring attached with its one end to the back of said blackboard, with its other end to a connecting rope attached to a point in the groove of said cam disc having the greatest radius thereof, said cam disc being designed thus that its radius decreases, starting from said end attachment point for said connecting rope, inversely proportionally to the increasing of the tensioning of said spring on lowering the blackboard, whereby the whole movable pulley, cam disc and rope mechanism remains hidden from the pupils regardless of the extent of the shifting of the blackboard.

References Cited by the Examiner UNiTED STATES PATENTS 2,168,209 8/1939 Haupt 74592 X 3,037,301 6/1962 Siepel 35-63 3,144,229 8/1964 Wolters 3563 X EUGENE R. CAPOZIO, Primary Examiner.

HARLARD SKOGQUIST, Assistant Examiner. 

